The present disclosure relates to a power-supply device that converts a supplied DC voltage by switching with a switching element, and supplies the converted DC voltage from an output terminal to an external battery.
Vehicles such as hybrid vehicles and electric vehicles include a driving motor and a high-voltage battery for supplying power to the driving motor. The output voltage of the high-voltage battery is provided to the driving motor after being boosted by a voltage-boosting converter, and provided to auxiliary devices after being stepped down by a step-down converter.
FIG. 1 is a block diagram showing an example of a configuration of a major part of a conventional power-supply device 5C for use in such a hybrid vehicle or an electric vehicle. The power-supply device 5C includes a DC/AC conversion circuit 51 that converts DC voltage from a high-voltage battery 4, which is connected to the outside via system relays SRB and SRG, to AC voltage, a control circuit 52 that generates a control signal for turning on or off a MOSFET (hereinafter referred to as “FET”) 511 provided in the DC/AC conversion circuit 51, and a driving circuit 53 that drives the FET 511 with the use of the control signal.
The AC voltage generated through conversion by the DC/AC conversion circuit 51 is stepped down by an isolation transformer 54 and rectified by a rectifier circuit 55, and the rectified DC voltage is smoothed by a smoothing circuit 56 and then supplied from an output terminal 501 to a low-voltage battery 6, a power supply ECU 7 and an unshown low-voltage load (auxiliary devices) that are provided outside. Low operating voltage is supplied to the control circuit 52 and the driving circuit 53 from a converter circuit 57 that converts the voltage of the high-voltage battery 4. The control circuit 52 detects voltage applied to a voltage terminal 502 in response to an ignition (IG) relay contact 61 being controlled to be on by the power supply ECU 7, and starts generating the aforementioned control signal. The control circuit 52 is also configured to notify the power supply ECU 7 of a power supply failure signal if a failure is detected in the power-supply device 5C.
The aforementioned power-supply device 5C is problematic in that low operating voltage is supplied from the converter circuit 57, which is connected to the high-voltage battery 4, to the control circuit 52 and the driving circuit 53 that need to be electrically isolated from circuitry provided on the high-voltage battery 4 side, and thus complex and expensive circuitry is required.
To address this, Japanese Patent Application 2003-284320A discloses a DC-DC converter for automotive use in which operating voltage for a control circuit and a voltage detection circuit, which respectively correspond to the control circuit 52 and the driving circuit 53 shown in FIG. 1, is supplied from an auxiliary power supply (low-voltage battery) connected to output terminals of the DC-DC converter via a switching means. This configuration eliminates the need to provide a separate power supply such as the aforementioned converter circuit 57. In addition, by controlling the switching means to be off by an external ECU while the DC-DC converter is not performing voltage conversion, unwanted discharge of the low-voltage battery connected to the output terminals of the DC-DC converter is prevented.